Genetic Basis of Inheritance
Short Questions and Answers
One Mark Questions with Answers
1. A recessive trait in garden pea is
(a) wrinkled seeds
(b) tall stem
(c) ground seeds
(d) coloured seed coat
Answer: (a) wrinkled seeds
2. Hybrid vigour is due to
(a) mixing of traits of male and female
(b) homozygosity in gamete state
(c) superiority of genes
Answer: (d) heterozygosity
3. Which is connected with multiple phenotypes?
(c) polygenic inheritance
Answer: (b) pleiotropy
4. In Mirabilis jalapa, crossing of red flowered and white flowered plants yield pink flowered plants. This is due to
(a) crossing over
(b) complete dominance
(c) incomplete dominance
Answer: (c) incomplete dominance
5. Mendel did not observe linkage due to
(c) crossing over
(d) independent assortment
Answer: (d) independent assortment
6. Sickle cell anaemia is an example of
(d) incomplete dominance
Answer: (c) pleiotropy
7. If both parents are albino, all the offspring shall be
(b) some albino some normal
(c) homozygous normal
(d) heterozygous normal
Answer: (a) albino
8. Albinism is due to non synthesis of melanin on account of absence of
Answer: (c) tyrosinase
9. Which is correct about trait chosen by Mendel?
(a) terminal pod is dominant
(b) constricted pod is dominant
(c) green coloured pod is dominant
(d) tall plants are recessive
Answer: (c) green coloured pod is dominant
10. Most favourite and ideal material for researches in genetics is
Answer: (d) fruitfly
11. Epistaxis is due to
(a) interactions of two alleles of the same gene
(b) interaction of two separate genes
(d) multiple alleles
Answer: (b) interaction of two separate genes
12. The symbol of empty circles used in pedigree analysis represents
(a) normal females
(b) normal males
(c) affected females
(d) affected males
Answer: (a) normal females
Two Marks Questions with Answers
1. Define F1 and F2 generations.
Answer: F1 or first filial generation is the generation of hybrids produced from a cross between the genetically different individuals called parents. For example,Tt individuals are produced in F1 generation from a cross between TT and tt parents.
F2 generation or F2 second filial generation is a generation of individual which arises as a result of inbreeding or interbreeding amongst individuals of F1 generation.
2. If two individuals of intermediate skin colour marry how many phenotypes of skin colour are possible?
Answer: When two individuals of intermediate colour marry, the skin colour of children will vary from very dark to black to very light or white. A total of 8 allele combinations is possible in the gametes forming 27 distinct genotypes distributed into 7 phenotypes.
3. Do variations appear in clones also? How?
Answer: Variations do appear even in the clones. They are of two types, acquired and mutations. The acquired variations are usually due to the effect of environment. They are not inherited. Differences appearing in monozygotic twins are also acquired variations. Mutations are sudden or discontinuous inheritable variations which are produced due to changes in the genetic constitution.
4. What is polygene?
Answer: A polygene is defined as a gene where a dominant allele controls only a unit or partial quantitative expression of a trait. It is also termed as a gene in which a dominant allele individually produces a slight effect on the phenotype but in the presence of similar other dominant allele controls the quantitative expression of a trait due to cumulative effect. Hence, polygenes are also called cumulative genes.
5. Differentiate between monogenes and polygenes.
Answer: Monogenes produce discontinuous variations in the expression of traits while polygenes produce continuous variations in the expression of traits. Monogenic inheritance controls qualitative traits while polygenic inheritance controls quantitative trait. In case of monogenic inheritance a single dominant allele expresses the complete trait while in polygenic inheritance a single dominant allele expresses only a unit of the trait.
Three Marks Questions with Answers
1. How light can cause variations in different plants and animals?
Answer: In the absence of light the plants remain etiolated. Shade produces elongated internodes and thinner and broader leaves. It increases the succulence of many vegetables. Strong light on the contrary helps in the production of more mechanical tissue and thicker leaves. Palisade parenchyma becomes multilayered under strong light but remains single layered under moderate intensities of light, example, Peach. The effect of light has also been observed by Cunningham in flat fish Solea. The fish habitually rest on left side It develops pigmentation and eyes on right side, the side exposed to sun. If left side is exposed to sunlight in the young fish both eyes and pigmentation develop on that side.
2. What do you understand by phenotype and genotype? Explain by giving example.
Answer: Genotype: The gene complement or genetic constitution of an individual with regard to one or more characters irrespective of whether the genes are expressed or not. For example, the genotype of hybrid tall pea plant is Tt, pure tall TT and dwarf the patient.
Phenotype is observable or measurable distinctive structural and functional characteristics of an individual with regard to one or more characters which is a result of gene products brought to expression in a given environment. For recessive genes, the phenotype is similar to genotype. For dominant genes, the phenotypic expression can be due to its homozygous genotype of heterozygous genotype. For example, phenotypic tall pea plant can be genotypically TT or tt.
3. What is monogenic inheritance?
Answer: Monogenic inheritance is the type of inheritance in which a single dominant gene influences a complete trait. Presence of two such dominant genes does not alter the phenotype. The genes controlling inheritance are called monogenes, example, TT or Tt for tallness in pea. Qualitative inheritance produces a sort of discontinuous trait variations in the progeny, example either tallness or dwarfness. Intermediate forms or continuous trait variations are not produced.
4. What is polygenic inheritance?
Answer: Polygenic inheritance is a type of inheritance controlled by one or more genes in which the dominant alleles have cumulative effect with each dominant allele expressing a part or unit of the trait, the full trait being shown only when all the dominant alleles are present. The genes involved in quantitative inheritance are called polygenes. Quantitative inheritance is therefore also called polygenic inheritance. It is also named as multiple factor inheritance. A few instances of quantitative inheritance are kernel colour in wheat, cob length in maize, skin colour in human beings, human intelligence, milk and meat yield in animals, height in human beings and several plants, yield of crop plants including size, shape and number of seeds are fruit per plant.